The present invention relates to alternating current power regulators and more particularly to regulators providing regulated, substantially sinusoidal, alternating current to a variety of loads including but not limited to high intensity discharge lamps.
Present-day lighting applications require sophisticated control capabilities in order to minimize energy consumption and to provide for variable illumination needs of users. Control requirements are applicable to all kinds of lamps including incandescent lamps and electric discharge lamps such as fluorescent, mercury vapor, metal halide and high pressure sodium lamps. The most stringent control requirements are associated with a type of electric discharge lamps commonly known as high intensity discharge lamps.
High intensity discharge (HID) lamps such as metal halide (MH) or high pressure sodium (HPS) lamps are used in applications where large areas need to be lighted. Outdoor applications include street lighting, parking lot lighting. and stadium lighting. Typical indoor applications include warehouses, agricultural greenhouses and indoor arenas. It is desirable to be able to dim these lamps to save energy. On/off switching may be impractical, or may affect personnel safety, due to the approximately 20 minute warmup time required after turn-on before these types of lamps reach full intensity.
Conventional lamp dimmers are designed to work with incandescent lighting. Typical incandescent lamp dimmers employ thyristors to chop out a portion of each half cycle of alternating current (AC) sine wave supply current, thus reducing the amount of power delivered to the lamp. This approach is satisfactory for incandescent lamps because they are resistive in nature and have large thermal time constants which filter the abrupt change in lamp current without harmful effects to either the dimmer or the lamp. However, HID lamps, having an inherent negative resistance characteristic, require a high impedance source to ensure stable operation. The high impedance source is typically provided by an inductive ballast in series with the HID lamp. Conventional lamp dimmers employing half cycle regulation will not work satisfactorily with HID lamps because the rapid switching action of thyristors in combination with the inductive ballast results unacceptably large voltage transients.
A present approach to dim HID lamps is to use motorized Variacs(trademark) or variable transformers operating with elaborate control electronics. The large mass of Variacs(trademark) prevents real time line regulation and is prohibitively expensive except for very large installations. Another approach for dimming HID lamps is termed xe2x80x9cstep dimmingxe2x80x9d or xe2x80x9chigh-low dimmingxe2x80x9d. This latter approach employs switches to select various size inductors or capacitors in the ballast circuit to alter the HID lamp current. Another approach, frequently used in tunnels, achieves a crude dimming effect by turning off every second or third lamp.
HID lamps are required to operate in strict conformance with manufacturers"" operating requirements in order to achieve the utmost in lamp reliability. Typically, manufacturers require a specified warmup time before dimming is permitted, a cool-down time before re-ignition if the lamp arc has been lost and a maximum rate of dimming. Further, in order to achieve long lamp life and freedom from the lamp extinguishing during a brown-out, a dimmer should maintain a substantially constant output voltage despite wide and rapid power line fluctuations. Additional desirable characteristics of an HID dimmer include minimum injection of harmonics into the power line, the ability to sense a failed or removed lamp and programmable dimming.
The present invention is directed to providing an economical source of controlled power suitable for powering one or more incandescent lamps or ballasted electric discharge lamps. The present invention overcomes the problems inherent in the prior art by providing a solid state power regulator comprising a microcontroller capable of reacting to a multitude of command sources in combination with a voltage converter capable of supplying a regulated output voltage. The power regulator further provides the capability to respond to host computer commands, occupancy sensors, time-of-day dimming commands etc. and further includes the capability to adjust the xe2x80x9chighxe2x80x9d setting to 90% of maximum to take advantage of demand rebates. The power regulator implements manufacturer""s imposed HID lamp operating rules including a warmup period before dimming is permitted, a cool-down period before re-ignition if the lamp arc is lost and rate of time for dimming. In addition the power regulator maintains a constant voltage level to the HID lamps substantially independent of power line fluctuations, and provides for detection of lamp faults due to lamp aging or due to catastrophic failure.
The present invention comprises a power regulator for use with an AC power source comprising a voltage converter having a first input and a second input, the first input being connected with the AC power source and receiving AC current therefrom and the second input being connected with a controller and receiving a control signal therefrom. The voltage converter generates a substantially sinusoidal regulator output signal, the amplitude of which is responsive to the control signal. The power regulator also comprises a controller having a first input and a second input, the first input receiving the regulator output signal and the second input receiving a set point signal, the set point signal determining the amplitude of a substantially sinusoidal reference signal and the reference signal being substantially in-phase with the regulator output signal. The controller generates the control signal indicative of the instantaneous difference between the regulator output signal and the amplitude of the reference signal wherein the amplitude of the reference signal is independent of the amplitude of the AC power source and the amplitude of the regulator output signal.
The present invention also provides a power regulator for use with an AC power source for regulating the power applied to at least one lamp comprising a voltage converter having a first input and a second input, the first input being connected with the AC power source and receiving AC current therefrom, and the second input being connected with a controller and receiving a control signal therefrom, the voltage converter providing a substantially sinusoidal regulator output signal, the voltage of which is responsive to the control signal. The power regulator also includes a controller having a first input and a second input, the first input receiving the regulator output signal and the second input receiving a set point signal, the controller generating the control signal based on a status of at least one lamp and a comparison of the voltage of the regulator output signal with a substantially sinusoidal reference signal, the amplitude of the reference signal being responsive to the set point signal and independent of the amplitude of the AC power source and the regulator output signal. The controller determines the status of the at least one lamp by comparing an output current of the regulator with at least one predetermined fault limit.
The present invention also includes a method of generating a substantially sinusoidal output voltage for powering at least one lamp with a power regulator connected to an AC power source comprising the steps of determining a status of the at least one lamp; generating a substantially sinusoidal reference signal responsive to a set point and the lamp status; generating the substantially sinusoidal output voltage; generating a control signal responsive to the difference between the substantially sinusoidal output voltage and the sinusoidal reference signal such that output voltage is proportional to the sinusoidal reference signal if the lamp has a regulation status; setting the output voltage to full output if the lamp has a power-up status; and setting the output power to zero if the lamp has a cool-down status.